The effects of drugs on pupillary dynamics and function provide an assessable model for investigating neurophysiologic actions of drugs. For example, animal research at the ARC have utilized pupillary assessment to characterize the neural mechanisms of action of a range of psychomotor stimulants and opioids with affinities for different receptors. This research has been extended to clinical studies where the pupillary effects of several classes of abused drugs were compared to their performance and subjective effects. Additional research on retinal physiology using newly developed pupilometers has yielded new information of the retinal processing of the light reflex. Since retinal neural organization mimics brain neural systems, it is proposed that the influence of drugs in this system indicates drug mechanisms elsewhere in the brain. Dependent measures of these studies include pupil size, constriction and dilation velocities of the light reflex, smooth pursuit and saccadic tracking. These studies are typically within subject repeated measure design, when drugs are administered it is double blind and placebo controlled. Progress to date: The effects of marijuana, ethanol, cocaine, opiates amphetamine have been studies after various routes of administration.